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Figure 5.40 Total dissipation in the wave water column
T
a
(5.73)
versus measured total wind input
I
a
(denoted as
T
and
I
, respectively). Parameterisation
(5.68)
is used for integrating
D
a
in
(5.67)
at
z
>
0
.
6
H
s
. Figure is reproduced from
Babanin
et al.
(
2005
)
The outcome is shown in
Figure 5.41
and the resulting parameterisation for the dissipation
rate
dis
is now as follows:
⎧
⎨
const
z
≤
0
.
4
H
s
,
z
−
1
dis
(
)
=
z
∼
z
>
0
.
4
H
s
,
U
10
<
7
.
5m
/
s
,
(5.74)
⎩
z
−
2
∼
>
.
4
H
s
,
U
10
>
.
/
.
z
0
7
5m
s
sisevi-
dent as a threshold for breaking of dominant waves starting to occur (see also
Figure 9.3
and discussion in
Section 9.1.1
). The universality of this conclusion has to be further ver-
ified in larger water bodies (see also discussion in
Section 3.1
). Additionally,
Bortkovskii
(
1997
,
1998
), for example, points out that this wave-breaking threshold wind speed depends
on the water temperature. According to
Bortkovskii
(
1998
), the whitecaps start to appear
at a wind speed of 7m
Thus, based on the Lake George measurements, the wind speed of
U
10
≈
7
.
5m
/
sifitis0
◦
C.
Other roles of the wind can now be discussed. Wind action is important on longer
scales in altering breaking statistics because of enhancing the wave steepness. At moderate
winds, doubling the wind speed leads to achieving the limiting steepness and breaking four
s if the temperature is 30
◦
C and at 8
/
.
5m
/
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